1. Field of the Invention
The present invention relates to a method and a system for supporting construction when a continuous wall is formed in an underground, and an excavator therefor.
2. Description of the Related Art
The excavator for construction of an underground continuous wall comprises a traveling truck, and a cutter post hung down into the underground from the truck. Trenching is carried out while rotating a chain type cutter 52 using the cutter post as a guide.
The steps for the method for construction of underground continuous wall using the above excavator will be explained in order.
i) Step of Excavation
As shown by the dash-dotted contour line in FIG. 15a, a cutter 52 is placed into the excavated longitudinal trench. The traveling truck (not shown) is being moved in an excavating direction while rotating the cutter 52 to thereby excavate a continuous trench B1. Excavating liquid C is poured into the trench B1 in order to retain the shape of the trench B1.
ii) Step of Pouring Solidifying Liquid
As shown in FIG. 15b, the cutter 52 is returned to a starting end of the excavation while pouring ground solidifying liquid D into the trench B1. The ground solidifying liquid D and the excavating liquid C are stirred and mixed making use of the rotation of the cutter 52.
iii) Step of Re-stirring and Mixing
As shown in FIG. 15c, the cutter 52 is moved to an ending side of the excavation while rotating the cutter. Thereby, the ground solidifying liquid D and the excavating liquid C are further stirred and mixed. Thereafter, when soil cement which is a mixture of both the liquids C, D and the earth and sand resulting from excavation is solidified, a soil cement wall E is formed.
iv) Step of Next Excavation
As shown in FIG. 15d, a new trench B2 is excavated from the end of the formed soil cement wall E. The continuous soil cement wall E is formed by repeating the above-described steps.
However, the construction know-how has not been established yet, and the ground different in properties in the depth direction is excavated, which poses a problem that the construction predication is hard to establish.
Whether or not the construction of the underground continuous wall progresses as scheduled often depends upon the ground conditions. How to operate the excavator according to the ground conditions depends on the experiences of a field worker and the know-how, and if mistake is made on the judgment, the term of works is delayed.
In case the construction depth is deeper, the cutter post is left within the excavated trench even the excavating construction in that day has been completed. Further, unless the cutter post is in the state that the edge is fully cut with respect to the end of the soil to be excavated, there occur troubles such that at the start of operation, the cutter post flexes and is broken.
On the other hand, aging work is carried out when the construction of excavation is completed. The object thereof is to move the cutter post away from the soil, to remove a bend of the cutter post in advance, and to leave the cutter post at a position of pouring ground solidifying liquid, that is, a position sufficiently away from the land-making end.
The aging work and the friction cutting work are also carried out, in the present condition, on the basis of the experiences of an operator, and carrying out excavation efficiently is a most difficult task.
It is an object of the present invention to provide a method for supporting excavating construction for supporting so as to carry out construction of an underground continuous wall as scheduled, an excavator used therefor, and a construction supporting system.
The excavation supporting method according to the present invention carries out, in the construction of underground continuous wall carried out by inserting an excavating member into a cutter post, and moving the cutter post in a lateral direction while operating the excavating member to thereby form an excavated trench, supporting by the following procedures.
The distribution of ground strength of the ground to be excavated is obtained in a direction of depth. The accumulated ground strength is obtained from the distribution of ground strength. The necessary excavating ability of the cutter post balanced with the excavating resistance obtained from the accumulated ground strength is obtained. The thus obtained necessary excavating ability is compared with the excavating ability of the excavator used in the work site, and the excavating efficiency is evaluated on the basis of the compared result.
For example, the strength distribution of the ground to be excavated is first obtained in the direction of depth on the basis of the property of ground obtained by drilling survey, and the accumulated ground strength is obtained from the strength distribution. The accumulated ground strength will be the ground resistance exerting on the cutter post at the time of excavation. When the excavating work is carried out, the necessary excavating ability of the cutter post balanced with the accumulated ground strength is calculated. As a result, the minimum excavating force as the minimum value of the excavating force that may compete with the accumulated ground strength is obtained. Accordingly, control may be made so as to have the excavating ability more than that mentioned above.
Comparing the necessary excavating ability with the excavating ability of the excavator carried into the work site, the fact that the ground to be excavated can be excavated by ability of what % of rated value can be evaluated. For example, in case of soft excavating ground, the evaluated value of the excavating ability is small. In this case, it is expected that the construction is carried out as scheduled.
Conversely, in case of hard excavating ground, the evaluated value is large. In this case, in order to be in time for the term of works, means may be employed in which the excavator is operated at the upper limit of ability, or the excavating ability is saved to extend the operating time.
Accordingly, since the excavating efficiency is evaluated as described above, it is possible to make an accurate excavating construction plan according to the ground to be excavated.
Further, carrying out of the aging work or the friction cutting work in the above construction is well suited.